Shielded spark plug



April 23, 1935. A. s, slMsAcK SHIELDED SPARK PLUG Filed April 3, 1954 i perfomance.

Patented Apr. 23, 1935 UNITED STATES PATENT OFFICE` 8 Claims.

This invention relates to spark plugs for the ignition system of an internal combustion engine and, more particularly, to spark plugs for use in engine-propelled vehicles equipped with radio receivers such as automobiles, aeroplanes, motor boats, etc.

As new well known, the ignition .system of an internal combustion engine sets up high frequency disturbance oscillations which deleteriously affect the operation of a radio receiver carried by a vehicle being propelled by the engine. The spark plugs and the lead-in conductors therefor are the major offenders, as they act as small radiating antennae for the disturbance oscillations. Heretofore, suppressor elements, usually in the form of carbon resistors, have been inserted in the spark plug lead-in conductors for the purpose of suppressing or damping the disturbance oscillations. These elements have not been very satisfactory, however, and they are objectionable because their inclusion in the ignition system affects the engine Attempts have also been made to shield the spark plugs but without much success.

'Ihe principal object of the present invention is to provide an improved shielded spark plug which is adapted to completely shield the ungrounded electrode of the plug and which is particularly adapted for use with a shielded lead-in conductor and is designed to adequately ground the shielding of the conductor as well as the shielding elements of the plug.

Another object of the invention is to provide an improved shielded spark plug in which a simple but efficient electrical connection of the leadin conductor to the ungrounded electrode is made inside the plug so that there is no external connection.

A further object of the invention is to provide an improved shielded spark plug in which pro- `vision is made for securely clamping the end of the shielding armor or sheath of a shielded leadin conductor so as to electrically connect the same to the shielding elements of the plug and, at the same time, insure good electrical contact between the conductor core and the ungrounded electrode of the plug.

i still further object of the invention is ,to provide an improved shielded spark plug having a metallic shell completely enclosing a body of porcelain such as is commonly used to support the ungrounded electrode, and having an expansion chamber separating the shielding shell from porcelain body throughout substantially the (CLN3-169) entire areas of the walls of these elements, so that breakage of the porcelain body, due to unequal expansion of the metal shell and the porcelain body, is prevented.

Other objects and features of the invention 5 will be apparent hereinafter as the description proceeds. In the drawing:

Fig. l is an elevational view of the improved spark plug and a portion of an associated shieldyl0 ed lead-in conductor;

Fig. 2 is a sectional view of the spark plug .taken through the center of the same;

Fig. 3 is a sectional plan view taken along line 3-3 of Fig. 2; and

Fig. 4 is a sectional plan view taken 4 4 of Fig. 2.

Referring to the several views of the drawing, and particularly to Figs. 1y and 2, the improved spark plug comprises essentially a metallic outer shell designated generally by reference character l and an insulating body 2 formed of porcelain or like material disposed Within the shell and completely enclosed thereby. The outer shell comprises a lower section 3 and an upper section 25 4. The lower section is similar to that found in the conventional spark plug. As is customary, the lower peripheral surface of this section is threaded, as at 5, for insertion in an internally threaded opening in the head of an internal combustion engine. At its lower end, -section 3 carries the usual grounded electrode 6. Section 3 is of polygonal formation at l to enable tightening by a wrench or other tool as is customary, and the upper portion of this section is internally threaded, as at 8, to receive the externally threaded lower portion Seof the upper section 4.

Section 4 is also of polygonal formation at I0 to enable tightening of the same within section 3. The upper portion of section 4 is formed as illus- 40 trated and is provided with a central opening into which a metallic cap II may extend. Section 4 and cap Il are preferably formed of metal which is softer than that of which section 3 is formed. For example, these elements may be formed of brass, copper, zinc, or any other similar material. Section 4 and cap Il are provided respectively with internal and external threadsY for cooperative engagement. The cap is formed so as to have a flanged head l2 which may be 50 lmurled to facilitate tightening of the cap. The cap has a central opening or bore through which the lead-in conductor I3 may extend.

Cap l i is recessed to provide an annular shoulder i4 so as to seat the upper end of an insulating 55 15 along line CTI against the annular shoulder I4 by the bushing.

I5. The stranded conductor core IB and the insulation I'I surrounding the core extend into the bushing as shown in Fig. 2. The end of the insulation abuts against the bottom of the bushing.

. The bushing is of elongated cup shape and is provided with a central opening in its bottom through which the conductor core may extend. The end of the stranded core is flared outward as at I8, and is pressed into engagement withthe head-like terminal I9 of the central ungrounded electrode 20. That is to say, the outwardly flared strands of the conductor core are clamped tightly between the end of bushing I5 and the electrode terminal I9.

The insulating body 2 is preferably formed as a unit and is shaped as illustrated to conform generally with the outer shell. The insulating body is centrally recessed at the top portion thereof to accommodate the insulating bushing and the end of the lead-in conductor. A central or axial bore is provided in the insulating body through which the electrode .20 extends, this electrode terminating at its lower end adjacent electrode 6 to give the usual spark gap. The insulatingbody Y and the electrode carried thereby are provided with complementary thread-like surfaces at 2l in order to securely lock the electrode within the body.

The outer metallic shell and the insulating body are of such relative sizes that there is provided an expansion chamber 22 separating the shell from the body throughout substantially the entire area of the walls of these elements. The lower section 3 of the shell is of enlarged internal diameter at 2S to accommodate the enlarged portion 24 of the insulating body. Preferably, a resilient metal gasket 25, which may be formed of brass or like material, is seated on the annular shoulder 2S of section 3 and the enlarged portion 24 of the insulating body is, in turn, seated on the gasket. This provides a resilient seating for the breakable insulating body and, at the same time, serves to center the same within the outer shell. The lower end of section 4 of the outer shell may engage the enlarged portion of the insulating body. as at 2T, to hold the body firmly in place. The engagement of the metallic shell with the breakable insulating body at this point is of such relatively small area that there is no danger of breakage due to unequal expansion of these elements, particularly as the yieldable gasket 25 and the resilience of section 4 serves to prevent the application of breaking force to the porcelain body. Thus the insulating body is centered and held firmly at iis enlarged portion between resilientclamping surfaces. lf desired, however, a

yieldable gasket similar to gasket 25 be positioned between lire lower end of the shell section l and the enlarged portion of the porcelain body.

From the above description, it will be secn that the spark plug provided by this invention is simple in constructie i and ye performs its insistance between the conductor sheath and the grounded section 3. These ground joints are materially enhanced by the relatively soft metal construction of cap II and section 4, because the soft metal forms a better joint at each threaded attachment. At the same time, the ungrounded electrode of the plug, as well as the conducting core of the lead-in conductor, is completely and adequately shielded, thus preventing the radiation of disturbance oscillations which would otherwise affect the operation of a radio receiver carried by the vehicle.

It. will be seen that the construction of the plug permits ready attachment and detachment of a lead-in conductor thereto. As shown clearly in Fig. 2, the lead-in conductor may be detached by simply unscrewing cap II and then pulling the conductor from the upper recess of the porcelain body. As the insulating bushing I5 snugly engages the conductor insulation, the bushing may be removed with the conductor. In order to attach a lead-in conductor to the plug, it is simply necessary to cut back the shielding sheath and the insulation the desired amounts, insert the conductor through the detached cap II, slide the insulating bushing I5 over the end of the conductor insulation, and then insert the end of the Pconductor with the insulating bushing thereon into the recess of the porcelain body and tighten the cap II in place. The desired flaring of the conductor core and sheath may be brought about by simply exerting axial pressure on the conductor just prior to tightening cap II. The strands of which the conductor core and sheath are composed may be readily flared at their ends in this manner. The tightening of cap I2 forces the insulating bushing I5 against the flared end of the conductor core and also clamps the shielding sheath of the conductor between the bushing and the cap. Although the conductor is held tightly at the ilared end of its conducting core,

the clamping of the shielding sheath serves to additionally secure the conductor to the plug.

Although it is preferred to use a shielded conductor having a metallic sheath composed of closely-woven strands, as above mentioned, the

spark plug may be used with a lead-in conductor having a shielding sheath composed of metal foil or like material. When such a conductor is used, the desired clamping of the shielding sheath ls not so readily obtained but, by virtue of the flexibility of the metal foil, the sheath is always in contact with cap II and the grounding of the sheath is thus practically insured.

It is important to note that the adjustable attachment of cap II to the metal shell enables tightening of the parts to obtain good electrical connections whenever the electrical joints become loosened or the parts wear. Thus, it is possible by this construction to maintain the proper electrical connection of the lead-in conductor to the ungrounded electrode of the plug and also maintain complete shielding and good grounding of the conductor sheath.

Although the preferred form of the device has been illustrated and described herein for the pur vpose of disclosure, it will be understood that various changes and modiiications may be made within the scope of the invention which is defined by the appended claims.

I claim: 1. A shielded spark plug for a radio receiver equipped vehicle, comprising a metallic outer shell having an opening at the top thereof, an insulating body within said shell having a recess at the top portion thereof, an electrode extending through said body and terminating in said recess, a metallic recessed apertured cap through which an insulated electrical conductor may extend adjustably attached to said shell at the opening thereof, and an insulating bushing seated in said cap in cooperative relation therewith and extending into the recess of the insulating body, said bushing snugly surrounding said conductor and the cooperation between Asaid cap and said bushing forcing intimate contact between the end of the conductor core and the terminal of said electrode when said cap is adjusted.

2. A shielded spark plug for a radio receiver equipped vehicle adapted for use with a shielded insulated electrical conductor, comprising a metallic outer shell having an opening at the top thereof, an insulating body within said shell having a recess at the top portion thereof, an electrode extending through said body and terminating in said recess for engagement with the end of the conductor core, a metallic apertured cap through which said conductor may extend adjustably attached to said shell at the opening thereof and having an internal annular shoulder, and an insulating bushing seated in said cap and cooperating with the shoulder thereof to firmly clamp the end Aof the shielding armor of said conductor and electrically ground the same through said cap and said shell, said bushing extending into the recess of the insulating body and snugly surrounding the insulation of said conductor and pressing the end of the conductor core into iirm engagement with the terminal of said electrode.

3. A shielded spark plug for a radio receiver equipped vehicle adapted for use with a shielded insulated electrical conductor, comprising a metallic outer shell composed of upper and lower threadedly connected sections with an opening at the top of the upper section, and insulating body seated in said lower section and extending into said upper section with a recess at its top, an electrode extending through said body and terminating in said recess for engagement with the end of the conductor cor e, a metallic apertured cap through which said conductor may extend adjustably attached to said upper section at the opening thereof and having an internal annu-- lar shoulder, and an insulating bushing seated in said cap and cooperating with the shoulder thereof to rmly clamp the end of the shielding armor of said conductor and electrically ground the same through said cap and said shell, said bushing extending into the recess of the insulating body and snuglyV surrounding the insulation of said conductor and pressing the end of the conductor core into firm engagement with the terminal of said electrode.

4. A shielded spark plug for a radio receiver equipped vehicle, comprising a metallic outer shell composed of upper and lower threadedly connected sections, said lower section having an annular internal shoulder, a yieldable gasket seated on said shoulder, an insulating body formed of breakable material, such as porcelain, having a different coefficient of expansion than that of the metal shell,V said body having an enlarged shoulder portion the lower surface of which is seated on said gasket and the upper surface of which is directly engaged by the lower end of said upper section, and an expansion chamber of predetermined area separating the wall of said body from the wall of said shell at all points excepting at the aforesaid contact points between the enlarged shoulder of theinsulating body and the said gasket and between said shoulder and the lower end of the upper shell section, whereby breakage'of said body caused by the unequal expansion of said shell and said body is prevented.

5. A shielded spark plug for a radio receiver equipped vehicle, comprising a metallic outer shell composed of upper and lower threadedly connected sections, said upper section being formed of softer metal than said lower section, said lower section having an annular internal shoulder, a yieldable gasket seated on said shoulder, an insulating body formed of breakable material, such as poreclain, having a different coefficient of expansion than that of the metal shell, said body having an enlarged shoulder portion the lower surface of which is seated on saidgasket and the upper surface of which is directly engaged by the lower end of said upper section, and an expansion chamber of predetermined area separating the wall of said body from the wall of said shell at all points excepting at the aforesaid contact points between the enlarged shoulder of the insulating body and the said gasket and between said shoulder and the lower end of the upper shell section, whereby breakage of said body caused by the unequal expansion of said shell and said body is prevented.

6. A shielded spark plug for a radio receiver equipped vehicle, comprising a metallic outer shell having a screw-threaded opening at the top thereof, an insulating body within said shell having a recess at the top portion thereof, an electrode extending through said body and terminating in said recess, a metallic apertured cap through which an insulated electrical conductor I may extend, said cap being externally screwthreaded to cooperate with the opening in the metallic outer shell, whereby said cap may be relatively adjusted with respect to said shell, and an insulating bushing cooperatively arranged with said cap and extending into the recess of the insulating body, the cooperation between said cap and said insulating bushing after said cap is screwed into said shell maintaining electrical contact between the conductor core and the terminal of said electrode.

7. A shielded spark plug for a radio receiver equipped vehicle adapted for use with a shielded insulated electrical conductor.' comprising a grounded metallic outer shell having a screwthreaded opening at the top thereof, an insulating body within said shell having a recess at the top portion thereoLvan electrode extending through said body and terminating in said recess, a metallic apertured cap through which said conductor may extend, said cap being externally screw-threaded to cooperate with the opening in the metallic outer shell, whereby said cap may be relatively adjusted with respect to said shell. and an insulating bushing cooperatively arranged with said cap to firmly clamp the end of the shielding armor of said conductor between said cap and one end of said bushing after said cap is screwed into said shell, to electrically ground the said armour through said cap and said shell, said bushing extending into the recess of the insulating body and snugly surrounding the insulation of said conductor, the cooperation between said cap and said insulating bushing after said cap is screwed into said shell maintaining electrical contact between the conductor core and the electrode.

8. A shielded spark plug for a radio receiver equipped vehicle adapted for use with a. shielded insulated electrical conductor, lcomprising a grounded metallic outer shell having a screwthreaded opening at the top thereof; an insulating body within said she11;. an electrode extending through said body and having its upper end formed to provide a terminal; a metallic apertured cap through which said conductor may extend, said cap being externally threaded to cooperate with the opening at the top of said outer shell, whereby said cap may be relatively adjusted with respect to said shell; and an insulating bushing cooperatively arranged with said cap to firmly clamp between itself and the cap the end of the shielding armour of said conductor and thus electrically ground the armour through said cap and said shell, the cooperation between said cap and said insulating bushing maintaining the conductor core in electrical contact with the terminal of said electrode.

ANTON S. SIMSACK. 

